Tube for intensification of images



Dec. 14, 1954 E. E. SHELDON 2,697,182

TUBE FOR INTENSIFICATION OF IMAGES Original Filed Dec. 9, 1948 2Sheets-Sheet 1 Q Q? s I l mun Iii Cl Z3 3 JNVENTOR.

[ow/m0 Ema/10:4 $45400 i BY 6%; 5 my 9770mm y E. E. SHELDON TUBE FORINTENSIF'ICATION OF IMAGES Original Filed Dec. 9, 1948 2 Sheets-Sheet 2INVENTOR. [ammo [mm/a 5,951.00!

BY 924 6. M

2,697,182 Patented Dec. 14, 1-954 2,697,182 TUBE FOR EJTENSIFICATION FIMAGES Edward Emanuel Sheldon, New York, N. Y.

Original application December 9, 1948, Seriai No. 64,329, new Patent No.2,586,392, dated February 19', 1952. Divided and this applicationJanuary8, 1952, Seria! No. 265,466

4 Claims. (Cl. 313-65) My invention relates to the method and device forproducing X-ray moving pictures and represents a division of myco-pending patent application, Serial No. 64,329 filed on December 9,1948, now U. S. Pat. No. 2,586,392, issued February 19, 1952 and is acontinuation in part of The importance of cinematographic X-ray picturesto study the organs in health and disease was recognized long ago.Lately, the value of --ray moving pictures gained understanding inindustry in examination of moving parts of machinery. this method,

would represent only 2 seconds of cinematographic exposure, is the limitof safe X-ray application.

It is, therefore, the purpose of my invention to overshould be no hazardto the patient.

Another purpose of this invention is to reduce X-ray energy necessaryfor producing X-ray moving pictures in order to eliminate the need forexpensive and bulky multimillion volt X-ray equipment necessary forindustrial cinematograuhic studies.

Another obiective of my invention is to provide X-ray motion pictures fbetter detail and of greater contrast it Was possible until now.

The purposes of my invention were accomplished by the use in combinationof an X-ray source. an X-ray image intensifying tube, an optical systemand a moving picture camera. The invisible X-ray images of the examinedbody are projected onto a screen in which they are converted intofluorescent ima es. The fluorescent X-ray images are projected on anintensifying tube, in which they are converted into photoelectron ima eshaving the pattern corresponding to X-ray images. The photoelectronimages after intensification by cascade amplification, by electronicdiminuation'and by secondary emission, are reconverted into fluorescentimages having the pattern of original X-ray images, but of a fewthousand times greater intensity. The intensified fluorescent X-rayimages are The invention Will be better understood when taken which amore compact reflective optical system is shown.

States Patent Cfitice Figure 3" represents a variety of this invention,in which afaster reflective optical system is shown.

Figure 4 represents a modification of the image pick-up tube having asolid photocathode.

Figure 5 represents a modification of this invention, in which the imagetube is responsive to an enlarged fluorescen't' image.

Figure 6 represents a modification of the optical systen used incombination with the image tube responsive to an enlarged fluorescentimage.

eference will now be made to Fig. 1, in which is shown the X-ray source37, the examined fluoroscopic screen 39, the fluorescent X-ray image 40,the optical-system 411 and the image intensifying tube 48'. The X-raysafter the passage through the examined body form an invisible Y-rayimage, which isconverted in the fluoroscopic screen 39 in'tofluorescentX-ray image 40. T! e fluorescent image is projected by the reflectiveoptical system 41'- on thephotocathode 42 of the image intensifying tube&8. The optical system 41 in thisform of invention must have thegreatest possible speed as the fluorescent X-ray image 40 lS'Of a veryweak luminosity.

making the use, in this invention, of the optical system belongingto-the family of so-called Wide field fast cameras described by L. G.Henyey and Jesse L. Greeusteinin OSRD Report No. 4505 which opticalsystem canbe manufactured in quantity with necessary precision. Thisoptical system does not require aspherical correction plate and consistsessentially-of meniscus lens and ofthe concave spherical mirror.All'optical surfaces have a common center of curvature located atdiaphragm wliichlimits the entering light rays. I modified this opticalsystem for purposes of" my invention by using, in addition, a plane orconvex spherical mirror located between the reflecting surface of themirror and its nearest conjugate focus. The operation of this opticalsystem is shown in Fig. l. The fluorescent X-rey image is producedbyinvisible X-ray image on the fluoroscopic screen 39, which has curvedsurface in order to eliminate spherical aberration. The fluorescentlight rays pass through the meniscus lens 43 and are reflected byaluminized concave spherical mirror 44- havtube 48,

j the concave A The fluoroscopic screen 39, the optical system 41 andimage intensifying tube 48 are enclosed in light-proof box 47 infixed'position accomplished by micrometer adjustment screw 32, whichshifts the lens 43 47 in relation to the examined separate fluoroscopicscreen 3% attached outside of the box 47; The fluorescent X-ray imageproduces in the photoemissive photocathode 4212 a photoelectron image.The photoelectron image obtained from the photoemissive la er 42; whichmay be of materials such as caesium silver oxide. caesium with antimonyor bismuth or antimony in combination with lithium or potassium, isprojected on the first composite screen 49 of the amplifying sec tion 50having one or a few successively arranged amplitying screens 49 and 49a,by means of focusing magnetic or electro-magnetic fields 55, which arenot indicated in detail, since they are well known in the art and wouldserve only to complicate the illustrations. The amplifying compositescreens 49 and 492i consist of an electron nervious, light opaque.lightreflecting layer 51, an electronfluorescent laver'52, alighttransparent barrier layer and a photoemissivelayer 54. Fluorescentsubstances, which may be used for'the layer 52 of amplifying screens #39490 are zinc silicates; zinc sulphide, barium Sill.

pirate, calcium tungstate with; or withouttactivators, NaI:

body 38, the

concave spherical or KI. Another group of fluorescent substances, whichmay be used for this purpose comprises organic phosphors, such asanthracene, phenantrene or the like. The satisfactory photoemissivematerials for the layer 54 will be caesium oxide activated by silver,caesium with antimony or with bismuth, or antimony with lithium orpotassium. The barrier layer 53 between the fluorescent andphotoemissive surfaces can be an exceedingly thin transparent film ofmica, ZnFz, silicon or of a suitable plastic. The electrons emergingfrom the amplifying screen 49 are electron-optically diminished andfocused by means of magnetic or electro-magnetic fields 55 on the nextamplifying screen 49a. The electron images from the amplifying section50 are focused by magnetic or electro-magnetic fields 55a and areprojected on the target 56 where they are intensified by secondaryemission. The secondary electron image is diminished electron-opticallyby magnetic or electro-magnetic lenses 57 and is focused on the electronreactive fluorescent screen 58a producing intensified fluorescent imagehaving the pattern of the original X-ray image. The screen 58a hasbacking of a thin layer of aluminum 58b, which is transparent toelectrons, but not transparent to the light. In this way,back-scattering of light from the fluorescent screen 58a is prevented.

The intensified fluorescent images 58 appearing on the screen 58a of theX-ray intensifying tube 48 can be filmed by the movie camera 59 as theirluminosity is now strong enough to expose the film 60 in a frame time,despite the use of the very small amount of X-ray energy. The moviecamera is driven with the synchronous motor 23 at 15 to 30 frames/second according to the speed of motion of examined organs. The shutter61 in the camera has opening giving exposure time from to of a second.

In this way, X-ray motion pictures can be produced without the use ofexcessive amount of X-ray energy an with complete safety for the patientwhich was the main objective of my invention.

A more compact arrangement of this invention is shown in the Fig. 2. Theoptical system 62 consists here of aspherical correction plate 62a,concave spherical mirror 62b and of plane mirror 63. The plane mirror 63is placed at an angle between the reflective surface of the concavemirror 62b and its nearest conjugate focus. The intensifying tube 48 ispositioned outside of the axis of the optical system 62b, so that itdoes not obstruct the path of the fluorescent rays from the fluoroscopicscreen 64 through the optical system.

Another reflective optical system having still greater speed forproducing X-ray image pictures is shown in Fig. 3. The fluorescent lightrays from the curved fluoroscopic screen 65 pass through doublet lens 66and are reflected back by the concave spherical mirror 67. The reflectedrays pass again through the doublet lens 66 and are focused on the planemirror 78, positioned at an angle to the optical axis of the system. Theplane mirror 78 reflects fluorescent light rays on the photocathode 68of the image intensifying tube 69 placed outside of the optical systemin order not to obstruct the path of light through the optical system.The photocathode 68 must have a curved surface corresponding to thecurvature of the focal plane of the concave spherical mirror 67. Thisoptical system has an exceptional speed and contributes considerably toimprovement of sensitivity of X-ray motion picture camera. Thefluoroscopic screen, the optical system and the image intensifying tubeare enclosed in a light-proof box 70 in fixed position to each other toavoid need for focusing at each examination. The remaining components ofX-ray moving picture recording device, such as motion picture camera,intermittent mechanism shutter and synchronous motor are the same asdescribed above, and shown in Fig. 1.

Further improvements in sensitivity of the X-ray movie camera is shownin Fig. 4. In this variety of invention, the photocathode 71 of theintensifying tube 72 is positioned in the focal plane of the concavespherical mirror 73 while the remaining part of said image intensifyingtube is on the opposite side of the reflecting surface of said concavespherical mirror. The fluorescent rays from the fluoroscopic screen 74pass through meniscus lens 75 and are focused by the concave sphericalmirror 73 on the photocathode 71. This optical arrangement allows theuse of solid photocathode instead of translucent photocathode andresults in gain of photoelectron output by factor of 2. This isequivalent to the same gain in sensitivity of X-ray motion picturecamera and represents considerable improvement over other X-ray movingpicture cameras. The remaining components of X-ray moving picture cameraare the same as described above and illustrated in Fig. 1.

In some instances, it is advantageous to produce an enlarged X-rayfluorescent image in the photocathode of the image tube. In such a case,see Fig. 5, the fluoroscopic screen is disposed between the reflectingsurface of the concave mirror 81 and the aberration correcting element82. The reflective optical system produces enlarged image 84 of thefluorescent image 83 in the fluoroscopic screen 80. This enlarged imageis reflected by the X-ray transparent plane mirror 85 on the image tube86. The optical system used for the enlargement of the X-ray image mayhave many forms and modification, only some of which have beenillustrated and it is to be understood that many changes may be madewithout departing from the spirit and scope of the invention. The imagetube 86 used in this modification of my invention has a very largephotocathode 87, which is of size sufficient to respond to the enlargedX-ray image 34. The photoelectron image produced by the projection ofthe X-ray fluorescent image on the photocathode 87 is electron-opticallydiminished by magnetic, electrostatic or electro-magnetic fields 88,which are not indicated in detail, as they are well known in the art,and is projected on the first composite screen 89 of the amplifyingsection 90. By electron-optical demagnification of the previouslyenlarged X-ray image, I obtained much better intensification of saidX-ray image than with previously described methods, because electronicintensification is proportional to the square of linear diminution. Theremaining parts of the image tube 86, as well as the motion picturecamera are the same as described above.

Another optical system for projection of an enlarged X-ray image isillustrated in Fig. 6. The optical system 96 in this case consists ofreflecting concave mirror 92 and of meniscus lens 93. The fluorescentX-ray image 94 is produced in the fluorescent screen 95, which ispositioned between the concave mirror and the meniscus lens 93. Thefluorescent X-ray image 94 is projected by the optical system 96 inenlarged form on the X-ray transparent plane mirror 97 and is reflectedtherefrom on the image tube 86 described above.

It will be understood that still X-ray pictures may be produced by myinvention in a similar manner, as described herein before for takingmotion pictures. The motion pictures camera will be in such a casereplaced by a still pictures camera.

Although the preferred embodiments of the invention have been described,it will be obvious to those skilled in the art that various changes andmodifications may be made by those skilled in the art without departingfrom the true scope and spirit of the foregoing disclosure.

I claim:

1. An image sensitive tube comprising in combination a photocathode of aphoto-emissive material for receiving an image and converting said imageinto a first electron beam having the pattern of said image, a compositescreen consisting of a light opaque layer transmitting said electronbeam from said photocathode, a fluorescent layer adjacent said lightopaque layer for converting said electron beam into a fluorescent lightimage, a light transparent separating layer discontinuous from walls ofsaid tube and of a photoemissive layer receiving light from saidfluorescent layer through said separating layer and emitting in responseto said light the second electron beam having the pattern of said firstelectron beam and an electron reactive screen for receiving said secondelectron beam and converting said electron beam into an image.

2. In a vacuum tube in combination a photocathode for receiving an imageand converting said image into a beam of atomic particles having thepattern of said image, electron-optical means for demagnifying said beamto intensify said beam, and a composite screen for receiving saiddemagnified beam, said screen comprising a fluorescent layer on the sidefacing said demagnitied beam, a light transparent layer and aphotoelectric ayer.

3. In a vacuum tube in combination a photocathode for receiving an imageand converting said image into a beam of atomic particles having thepattern of said image, electron-optical means for demagnifying said beamto intensify said beam, and a screen for receiving said de- ReferencesCited in the file of this patent UNITED STATES PATENTS me Date Number NaKeck Oct. 24, 1939 Number 6 Name Date Morton Feb. 6, 1940 Rose Sept. 17,1940 Kallmann Mar. 14, 1944 Sheldon June 5, 1951 Hunter et a1. June 5,1951 Sheldon Feb. 19, 1952

1. AN IMAGE SENSITIVE TUBE COMPRISING IN COMBINATION A PHOTOCATHODE OF APHOTO-EMISSIVE MATERIAL FOR RECEIVING AN IMAGE AND CONVERTING SAID IMAGEINTO A FIRST ELECTRON BEAM HAVING THE PATTERN OF SAID IMAGE, A COMPOSITESCREEN CONSISTING OF A LIGHT OPAQUE LAYER TRANSMITTING SAID ELECTRONBEAM FROM SAID PHOTOCATHODE, A FLUORESENT LAYER ADJACENT SAID LIGHTOPAQUE LAYER FOR CONVERTING SAID ELECTRON BEAM INTO A FLUORESENCE LIGHTIMAGE, A LIGHT TRANSPARENT SEPARATING LAYER DISCONTINUOUS FROM WALLS OFSAID TUBE AND OF A PHOTOEMISSIVE LAYER RECEIVING LIGHT FROM SAIDFLUORESCENT LAYER THROUGH SAID SEPARATING LAYER AND EMITTING IN RESPONSETO SAID LIGHT THE SECOND ELECTRON BEAM HAVING THE PATTERN OF SAID FIRSTELECTRON BEAM AND AN ELECTRON REACTIVE SCREEN FOR RECEIVING SAID SECONDELECTRON BEAM AND CONVERTING SAID ELECTON BEAM INTO AN IMAGE.